Various kinds of rotating-operation types of writing tools have been conventionally known in which a front axial cylinder and a rear axial cylinder are separable and a tip portion of the writing tool is caused to protrude from a front portion of the front axial cylinder by a rotating operation of the rear axial cylinder. For example, JP 2007-320209 by the same applicant has disclosed an example of a rotating-operation type of writing tool in detail.
FIG. 9 is a sectional view of the rotating-operation type of writing tool disclosed in JP 2007-320209. This writing tool is a fountain pen 101 in which a tail crown 103 is arranged at a rear portion of a cylindrical body 102, and the cylindrical body 102 and the tail crown 103 form an entire cylinder 104. The cylindrical body 102 is formed by a front inner cylinder 105 and a rear inner cylinder, which are respectively covered (overlapped) by a front axial member 107 and a rear axial member 108, wherein the front inner cylinder 105 and the rear inner cylinder 106 are jointed to each other by a male screw portion 105a and a female threaded portion being threadably mounted on each other.
A hollow pipe 109 is mounted at a front portion of the front inner cylinder 105 of the cylindrical body 102. An elastic front-end member 110, which is made of a rubber, is mounted at a front portion of the hollow pipe 109. A lid 112 is arranged at an inclined front-end surface of the elastic front-end member 110 in such a manner that the lid 112 is closed by a snapping force of a torsion coil spring 111.
A coil portion 111a of the torsion coil spring 111 is pierced through by an axial rod 113 mounted on the hollow pipe 109. The axial rod 113 also pierces through winding-back portions 112, which are arranged at a lower end of the lid 112 so as to sandwich both sides of the coil portion 111a. Thus, the lid 112 can be opened and closed around the axial rod 113 serving as a fulcrum.
In addition, a bending-back portion 111b formed on a front-end side of the torsion coil spring 111 is engaged on an engaging portion 112b formed by bending an upper portion of the lid 112, and a rear arm portion 111c of the torsion coil spring 111 abuts on a side surface of the hollow pipe 109. Thus, the torsion coil spring 111 always biases the lid 112 toward the elastic front-end member 110.
A writing body 114, which has a structure of a fountain pen, is arranged in the cylindrical body 102. The writing body 114 has a pen body as a writing tip 114b at a front portion of a writing body base 114a, and an ink cartridge 114c containing ink for a fountain pen at a rear portion of the writing body base 114a. 
A coil spring 115 is arranged between a step 114d formed at an intermediate portion of the writing body base 114a and a rear end portion 109a of the hollow pipe 109. The coil spring 115 has a function to always bias the writing body 114 rearward. A guide protrusion 114e provided on the writing body base 114a is loosely fitted (slidably fitted) into a slide groove 105b formed on an inside surface of the front inner cylinder 105. Thus, the writing body 114 can move forward and rearward without any rotation.
A female threaded portion 116a of a tail-crown inner cylinder 116 is threadably mounted on a male screw portion 106b formed at a rear end of the rear inner cylinder 106.
A cam cylinder 117 having a spiral cam groove 117a is arranged in the tail-crown inner cylinder 116. A male screw portion 117b of the cam cylinder 117 is threadably mounted on a female threaded portion 103a of the tail crown 103, thereby the cam cylinder 117 is rotatable integrally with the tail crown 103.
A pushing member 118 is arranged in the cam cylinder 117. A cam protrusion 118a having a shape like a head portion of a protruding pin is provided on a side surface of the pushing member 118. The cam protrusion 118a is loosely fitted in the cam groove 117a, and also loosely fitted in a slit 116b formed on the tail-crown inner cylinder 116 in a longitudinal direction thereof. In the example shown in FIG. 9, two pairs of the cam groove 117a and the slit 116b are provided axisymmetrically, and two cam protrusions 118a are provided correspondingly to them.
A flange 118b, whose diameter is larger, is provided at a front-end portion of the pushing member 118. A rear end of the ink cartridge 114c of the writing body 114 is caused to abut on the flange 118b. The coil spring 115 always biases the pushing member 118 rearward via the writing body 114, so that an O-ring 119 made of a rubber and mounted on a rear portion of the flange 118b is caused to abut on a jaw portion 106c formed on an inner surface of the rear inner cylinder 106. Thus, as shown in FIG. 9, under a situation in which the writing tip 114b has been caused to withdraw into the cylindrical body 102, the lid 112 abuts on the elastic front-end member 110 so that the front portion of the cylindrical body 102 assures airtightness, and the O-ring 119 abuts on the jaw portion 106c so that the rear portion of the cylindrical body 102 assures airtightness. Thus, as a result, the inside space of the cylindrical body 102 is closed sealingly.
Next, FIG. 10 shows a situation in which the writing tip 114b has been caused to protrude from the cylindrical body 102a. 
When the tail crown 103 is rotated in a clockwise direction (in a direction shown by an arrow in FIG. 10), the cam cylinder 117 is also rotated in the clockwise direction integrally, which creates a force to rotate in the clockwise direction the cam protrusion 118a loosely fitted into the cam groove 117a of the cam cylinder 117. Herein, the cam protrusion 118a is also loosely fitted into the slit 116b of the tail-crown inner cylinder 116. Therefore, the cam protrusion 118a cannot be rotated in the clockwise direction. Instead, the cam protrusion 118a is slidably moved forward in the spiral cam groove 117a while being guided by the slit 116b. 
Accordingly, the pushing member 118 is caused to move forward together with the cam protrusion 118a, so that the writing body 114 abutting on the pushing member 118 is also caused to move forward while compressing the coil spring 115. Subsequently, the writing tip 114b opens the lid 112, and the writing tip 114b protrudes from a front-end opening 107a formed at a front end portion of the front axial member 107.
After the writing tip 114b has protruded from the front-end opening 107a, the cam protrusion 118a of the pushing member 118 is held in a holding groove 117c provided adjacently to the cam groove 117a. Thus, the protruding condition of the writing tip 114b is maintained. The holding groove 117c is formed in a manner to go back a little in the axial direction of the cam cylinder 117 from the front end of the spiral cam groove 117a. Thereby, when the cam protrusion 118a is biased rearward in the holding groove 117c by the coil spring 115, the cam protrusion 118a is caught.
When the tail crown 103 is rotated in the opposite direction (anticlockwise direction) from the situation shown in FIG. 10, the cam protrusion 118a of the pushing member 118 is released from the holding groove 117c of the cam cylinder 117. Subsequently, by means of the elastic force of the coil spring 115, the cam protrusion 118a is subjected to a force in a direction opposite to that when the cam protrusion 118a has moved forward. Thus, the cam protrusion 118a moves rearward in the cam groove 117a while giving an opposite rotating force to the cam groove 117a. The pushing member 118 also moves rearward, and thus the writing body 114 that is biased by the coil spring 115 moves rearward, too. The impact that the writing body 114 may receive when the writing body 114 moves rearward is cushioned by the O-ring 119 mounted on the pushing member 118 abutting on the jaw portion 106c of the rear inner cylinder 106.